Bio: Cladistics

Cladistics is a method of classification of animals and plants according to the proportion of measurable characteristics they have in common.

• A clade is a group of organisms with a common ancestor. Evidence for this grouping comes from genetics, proteins, analogous & homologous traits

  

• Sequence differences accumulate gradually, so there is a positive correlation between the number of differences and the time since divergence from a common ancestor.

• Cladograms are tree diagrams that show the most probable sequence of divergence in clades and provide further insights into evolutionary relationships beyond morphological patterns

Rules for making/reading cladograms

• Extant organisms are found on a horizontal line at the top

• Extinct organisms are found lower down in the cladogram

• Branching points indicate the last common ancestor between species

• A key trait or some other evidence for evolution must be placed between organisms on a cladogram

• They can be diagonal or branched

Evolution of Life and Cladograms

• Useful tools to help us understand the origin of life and the divergence of difference of species

• One key idea in the formation of cladograms and other kinds of evolutionary tree diagrams is the assumption that all of life evolved from a common ancestor

• This shared common ancestor was formed about 4 billion years ago (Earth is about 4.6 billion years old) and is known as LUCA

• LUCA (last universal common ancestor) is the ancestor of all life on Earth today

• It likely lived in extreme environments: Evidence suggests that it may have thrived in hydrothermal vents or other harsh environments with no oxygen, using chemical reactions to produce energy

• Genetic evidence connects all life to LUCA: By studying DNA and the similarities in the genetic code of different species, scientists have concluded that LUCA passed down essential traits like the ability to build proteins and replicate genetic material